Synthetic resins have conventionally been widely used, for example, for construction materials, automobile parts, packaging materials, agricultural materials, housing materials for home appliances, and toys because of their excellent chemical and mechanical characteristics. Unfortunately, many synthetic resins are flammable and thus need flame-proofing for some applications. A widely known flame-proofing method is to use one or a combination of flame retardants, such as halogen-based flame retardants, inorganic phosphorus-based flame retardants typified by red phosphorus and polyphosphate-based flame retardants such as ammonium polyphosphate, organophosphorus-based flame retardants typified by triaryl phosphate ester compounds, metal hydroxides, and antimony oxide and melamine compounds which are flame-retardant assistants.
Particularly, flame retardants known to have excellent flame retardancy include intumescent flame retardants, i.e., flame retardants that include a salt between polyphosphoric acid or pyrophosphoric acid and a nitrogen-containing compound as a main component and that form a surface-swelling (intumescent) layer on combustion, thus achieving flame retardancy by preventing the diffusion of decomposition products and the transfer of heat. For example, Patent Literature 1 discloses such a flame retardant.
Patent Literature 2 proposes a flame retardant including, in combination, a nitrogen compound such as melamine phosphate or ammonium polyphosphate, and a bicyclic phosphate compound.
Unfortunately, these conventional flame retardants have insufficient flame retardancy, and have a drawback in that a large amount needs to be added to impart sufficient flame retardancy to a synthetic resin. However, the addition of a large amount of flame retardant, and/or poor dispersibility of the flame retardant to synthetic resin, may give rise to a need for a longer processing time, higher processing temperature, and increased screw rotation speed in a processing machine. This may overheat the resin, thus resulting in defective molding, such as foaming, and other problems in processability. Thus, there is a demand for a flame retardant having excellent flame retardancy and processability.